Fix migration error on database with zero IDs
Fix Mocha deprecation error
Change DEFAULT_SRID from -1 to 0

Fixes an annoying error message that gets spewed out during rspec runs:

NOTICE:  SRID value -1 converted to the officially unknown SRID value 0
Fix deprecation warnings in ObservationsController
Merge pull request #169 from md5/dev-fixes

Dev fixes